We have analysed the standards of the MK
system in the B0-F5 spectral region with the help
of Hipparcos parallaxes, using only stars for
which the error on the absolute magnitude is ≤ 0.3
mag. The sample stars (about one hundred) were
scrutinized for companions and for interstellar
extinction. We find that the main sequence is a
wide band and that, although in general giants and
dwarfs have different absolute magnitudes, the
separation between luminosity class V and III is
not clear. We conclude that there is no strict
relation between luminosity class and absolute
magnitude. The relation is only a statistical one
and has a large intrinsic dispersion.
We have analysed similarly the system of
standards defined by Garrison and Gray (1994)
separating low and high rotational velocity
standards. We find similar effects as in the
original MK system.
Evolution of Early-Type Galaxies in Clusters